Mold drying method and apparatus



-I I i Mi ka u HQ wwh l Ha H. F. HAGEMEYER MOLD DRYING METHOD ANDAPPARATUS Original Filed July 22, 1936 INVENTOR HENRY F. HAGEMEYERATTORNEY 7 llslimlui Patented June 25, 19

2. 205550 MOLD DRYING METHOD AND APPARATUS Henry F. Hagemeyer, Chicago,Ill., assignor tov Castings Patent Corporation, a corporation ofIllinois Original application July 22, 1936, Serial No. 91,897. Dividedand this application May 5, 1938, Serial No. 206,151

17 Claims.

My invention relates to the drying of articles composed of plasticmaterial and particularly the drying of complemental mold sections madeof a gypsum base composition. This application is a I i division of myapplication Serial No. 91,897, filed 5 July 22, 1936, for Dryingapparatus.

Mold sections well adapted to be dried by th herein-described method andapparatus may be made by the process described in my copendingapplication Serial No. 203,872, filed April 23, 1938, for Moldingprocesses. Itis desired that such molds have a body of high porosity sothat when two complemental mold sections are placed with their partingsurfaces in contact and metal is poured between them through the usualsprue,

the air in the mold spaces and the gases generated by the molten metalmay ooze out through the pores of the mold body without appreciableresistance to the inflowing metal even though no riser or other positiveegress aperture communieating with the mold space'is provided.

I have found that a very porous mold body,'suitable for my purpose, maybe constructed by using a large excess of liquid, preferably water, inthe plastic mixture and then drying out such excess liquid before thepour is made. The commercial value of such a scheme is greatly enhancedby my invention, for by the application of direct radiant heat to atleast theprincipal surfaces of the mold the free liquid or water may bedried from the mold in about an hour or at most a few hours, instead ofthe drying requiring several days as has been often required heretofore.Moreover,

my drying method may be regulated so that even l with such'rapid dryingthe mold will not crack or check or exhibit other physical defects. In.

luring its strength or other physical properties It is more specificallyan object to dry the mold by the application thereto of direct radiantheat as distinguished from circulating or convection heat, and to applysuch heat to at least the principal surfaces of each mold section.

A further object is to remove from the vicinity of the mold surfaces asrapidly as possible the v liquid vapor as it is released from the mold,thus to avoid the presence of a gaseous, heat absorbing,

insulating layer between the mold and the radiant heating surfaces, andto provide suitable means to accomplish this purpose. e

Other objects of my invention will be understood from a study of thefollowing detailed description of an operative example of my method andapparatus, and the particular .novel features thereof are set forth inthe appended claims.

Fig. 1 is a side elevation view of a drying oven showing parts thereofin section.

Fig. 2 is a transverse section of the oven taken along the line 2-2 ofFig. 1, and Fig. 3 is a perspective view of a mold section adapted to bedried in the oven- While my method and apparatus is adapted to dryproducts of similar type, it is particularly useful in drying moldsections made by the process described in detail in my aforesaidcopending application for molding processes. In the manufacture of suchmolds the drying problem is particularly acute, for unusually greatporosity is obtained by using in the mix a very excessive amount ofliquid which must be dried out of the mold after it has set, yet thesurface of the mold ,is relatively non-porous, largely owing to thedrying method employed.

The mold is of the gypsum base type, the dry material including calcinedgypsum, and the mix ing binder such as asbestos pulp or fiber. I

have found a'suitable mix, for example, to be, by weight, one hundredsixty parts of water to one hundred parts of dry material, the latterbeing eighty percent calcined gypsum and twenty percent asbestos pulp.From a mold made of such ingredients by my process and using myapparatus the liquid or water may be dried quickly and effectivelywithout injuring or appreciably weakening the mold.

In the preparation of a mold section ahomogeneous mixture is formed asdescribed in my previously mentioned application and allowed to set in amold form. This form is then completely removed from the set plasticmold section leaving it wholly unconfined. The mold section is thenready to be dried by my method without first be ing assembled withanother mold section. During the drying operation, preferablynot only isall the sensible liquid or free water dried out, but also some of thewater of crystallization chemically combined with the gypsum, perhapseven sufl'lcient to reduce the gypsum again substantially to thecalcined form. The act of removing water of crystallization orchemically combined water from the set gypsum is known as recalcination.

. The drying oven illustrated includes a body I having in its centralportion the drying chamber it Within which are received-molds M. Thesemolds, supported on grids II, are preferably moved through the oven fromend to end in the direction indicated by conveyor chains 12 driven bysuitable mechanism as shown. The grids are of special construction tosupport the molds so that they will remain unwarped during drying andwill not stick to the grids. The grids and related structure areparticularly described in my copending application Serial No. 206,150,filed May 5, v1938, for' Drying apparatus and methods.

The top and bottom walls l3 and "I4, respectively, of the drying chamberIII, are heat radiating surfaces preferably formed of silicon carbide,but which may be of any suitable heat conducting and radiating materialsuch as various steel alloys. Above the wall l3 and below thewall Mheating chambers are provided, designated l5- and it. These chambers mayextend over the entire length of the chamber I, but preferably only overthe entrance portion thereof, the exit portion being covered with sheetmetal enclosed chambers 20 and 2|, preferably forming continuations ofchambers I5 and i6, respectively,

but not being directly heated, to enable the mold leaving the dryingchamber. The stresses which would be set up in a hot mold by the shockof suddenly being moved into a relatively cold atmosphere are therebyavoided.

The heating chambers l5 and iii are heated bysuitable individuallyregulatable fuel jets or burners H which project into the sides of thechambers at spaced intervals along its length and are provided withsuitable air supply means for supporting the combustion of the gas oroil vapor. The -hot gases i may be required to traverse a tortuous path,if desired, to heat the imperforate radiating plates I3 and I 4 evenlyby providing suitable baflles. 'Heat is conserved by layers ofinsulation material l8, such as asbestos, covering the top and bottom ofthe oven adjacent to the heating chambers. The combustion gases passfrom such heating chambers to the uninsulated chambers 20 and M and areprogressively cooled as they pass therethrough by dissipation of heatthrough the uninsulated walls thereof until they. are discharged throughthe stack 22. The drying chamber is corresponding progressively cooledfrom the junction of the heating chambers and sheet metal coveredchambers to its exit by trans-. fer of heat therefrom and from the moldstherein to-the gradually cooling combustion gases. The molds are therebycooledgradually'to eliminate the shock of abrupt emergence from a hottea cold atmosphere upon discharge from thedrying chamber as previouslymentioned.

As seen inFig. 2 the extreme sides of the drying chamber III arepreferably closed by plates 3. Along the sidesof the-dryingchamberproper are aprons 3ii'extendingfrom the ceiling of the chamberdownward well below the upper surfaces of the mold sections. Below theseaprons are slots 3| along the opposite sides of the. drying chamberproper whichco'mmunicate with side passages or fiues 3 2 for a purposehereinafter explained. In some installations the sides 3 of the dryingchamber may be omitted, the mold containing portion thereof being indirect lateral communication with the atmosphere through the slots 3|.

In operation, a single Wet mold section M is placed upon each of thegrids H with its parting face upward, at the right hand end of the oven,.as shown in Fig. 1.

Upon entering the drying chamber the surfaces of the mold are subjectedto direct radiant heat from the plates t3 and it in close proximity tothe respective upper and lower mold surfaces, which are the principalsurfaces, preferably being spaced therefrom only a few inches. A smallamount of the hydrated gypsum is dissolved in the free water in the wetmold. As

the sensible liquid in the molds vaporizes, the

vapor is formed and liberated mainly at the principal, or upper andlower surfaces of the molds and fiows, because of the increase inpressure caused by emission of such vapor, from the drying chamberproper laterally outward through the slots 3i beneath the aprons 30 intothe ducts 32, or, if the side plates 3 have been omitted, directly intothe atmosphere. The vapor, thus continuously and immediately uponliberation being removed from the vicinity of the mold, eliminates allsubstantial blanketing or'insulating of the principal mold surfaces fromthe heat. radiating action of the plates l3 and I 4. The heat is notunduly dissipated, however, for its tends to remain above or to riseinto the space above the lower edges of the aprons 30. Even if theseaprons were omitted, allowing hot air to escape, the molds would stillbe dried quite effectively by the radiant heat to which they aresubjected.

There is no appreciable convection drying action by thermal or forcedcirculation of air.

Heretofore it has been thought that molds and articles of gypsum baseand similar plastic material had to be air dried in a heated room andcould not be dried without injury by the application thereto directlyand proximately of radiant heat. Not only is the mold not injured by myradiant heat drying method, however, but a finer surface than would beexpected on such a porous body is obtained. Since the water vaporizeschiefly at the surfaces of the mold, the hydrated gypsum dissolved inthe free water is deposited at the surface as the liquid evaporates. Theresult is a finer and less porous surface, yet one which is sufficientlythin so that the pouring gases in the mold cavity have no difficultyescaping therethrough into the porous mold body.

It is desirable that the molds move continuously past the radiantsurfaces during the drying operation. This movement assists in freeingthe vapor or steam from. the mold surfaces,

After all the free liquid is vaporized at least a' partial recalcinationof the mold material takes place'. The interior of a mold during thisoperation finally reaches a temperature preferably between 340 degreesF. and '420 degrees F. The temperature of the exterior surfaces wiil behigher since the-heat radiant surfaces are-much hotter thanthis. 'Whenspaced about four inches from the mold surfaces, for example, theirtemperature will be within a couple of hundred degrees .aboveor below1400 degrees R, which has been found to be the most suitable averagetemperature in such an installation for most gypsum base moldcompositions and mold shapes.

After molds thus dried are poured the recalcine'd material may bere-employed in the production of other molds, usually being mixedwithfresh calcined gypsum.

The complete drying operation for a mold section about two and one-halfinches thick may be performed in an hour and a half including passagethrough the portion of drying chamber ill adjacent to chambers 20 and 2|during which passage the molds are gradually cooled. For such dryingtime and temperature the over all length of the chamber l can be aboutthirtytwo feet, which includes both the entrance and exit portionsthereof. The heat is regulated so that each mold section is driedevenly, that is, the moisture withdrawn from the upper surfacewill beequal to the amount withdrawn from the lower surface in a given timeinterval and warping of the mold section will thus be avoided. It may benecessary to regulate compensably the temperatures of the two radiantsurfaces to obtaln this equal removal 'of' moisture from the oppositemold surfaces, owing to the unequal areas of the exposed mold faces andvariation of area of cavity surface in different molds, or to slightdifferences in proximity of the mold faces to the adjacent heat radiantsurfaces caused by varying mold thickness. Ordinarily, however,satisfactory operation may be obtained if the oven is regulated foraverage conditions of mold height and mold cavity surface.

As my invention, I claim:

1. The mold drying method which comprises exposing a suface of a gypsumbase mold for use as a casting matrix to a proximate source of directradiant heat, the temperature of such heat source and the time of moldexposure thereto being sufficient to dry from the mold all chemicallyuncombined liquid and also to recalcine, at least partially, the gypsumin the mold.

2. The mold drying method which comprises exposing a surface of a gypsumbase mold for use as a casting matrix to a direct radiant heatingsurface in close proximity thereto, and moving the mold in a pathsubstantially parallel to such heating surface during such exposure, thetemperature of such radiant heating surface and the time of moldexposure thereto being sufiicient to dry from the mold all chemicallyuncombined liquid and also to recalcine, at least partially, the gypsumin the mold.

3. The mold drying method which comprises simultaneously exposing theparting surface and the back of a gypsum base mold section for use as acasting matrix to proximate sources of direct radiant heat, thetemperature of such heat sources and the time of mold section exposurethereto being sufficient to dry from the mold section all chemicallyuncombined liquid.

4. The mold drying method which comprises simultaneously exposing thepartingsurface and the back surface of a gypsum base mold section foruse as a castingmatrix to substantially equal degrees of direct radiantheat applied substantially uniformly over each such surface, thereby topreserve the mold section unwarpedduring drying by substantially equaland concurrent evaporation of moisture from such opposite surfaces, themold section being heated by such radiant heat at a temperature and fora length of time sufficient to dry from the mold section all chemicallyuncombined liquid and also to recalcine, at least partially, the gypsumin the mold.

5. The mold drying method which comprises moving a gypsum base moldsection for use asv a casting matrix between parallel, radiant heatingsurfaces in close proximity thereto, thereby exposing the partingsurface and the back surface of such a mold section to substantiallyequal degrees of direct radiant heat applied substantiallyuniformly overeach surface, thereby to preserve the mold section unwarped duringdrying by substantially equal and concurrentevaporation of moisture from.such opposite mold surfaces, the temperature of such heating surfacesand the time of mold section movement therebetween being suflicient todry from such mold section substantially all the chemically uncombinedliquid 6. The mold drying method which comprises simultaneously exposingthe parting surface and the back surface of a gypsum base mold sectionfor use as a casting matrix to direct radiant heating surfaces in closeproximity thereto, the temperature of such heating surfaces and the timeof mold section exposure being sufficient to dry from the mold sectionsubstantially all chemically uncombined liquid, and removing the vaporreleased from the mold section laterally from the space between eachsuch mold surface and its adjacent heating surface as rapidly as mois-.ically uncombined liquid and also to recalcine, at

least partially, the gypsum in the mold section, and removing the vaporreleased from the mold section laterally from the space between eachsuch mold surface and its adjacent heating surface as rapidly asmoisture is liberated, thereby to minimize the blanketlng of the moldsurfaces from the radiant heating surfaces by such vapor.

8. In a mold drier, elements forming two radiant.heating surfaces-spacedapart to constitute a drying chamber, a support within the dryingchamber for positioning a mold section with each principal face adjacentto one of said sufaces. means to move said support lengthwise of thedrying chamber, and a duct extending lengthwise along the drying chamberto remove ,vapor escaping from the mold section laterally from suchchamber.

9. In a mold drier, elements forming upper and lower radiant heatingsurfaces spaced apart to constitute a drying chamber, a support withinthe drying chamber to position a mold section with each principal faceadjacent to one of said surfaces, and an apron extending lengthwis alongeach side of the drying chamber and depending from the roof thereof, thebottom edge of said apron being lower than the upper face of a moldsection positioned by said supportbut spaced above the drying chamberfloor to define a. slot'along the side of the drying chamber, for escapetherethrough of vapor dried from the mold section.

10. In a. mold drier, elements forming upper and lower, imperforateradiant heating surfaces spaced apart. to constitute a drying chamber,

heating means above the upper surface, and further heating means belowthe lower surface, to heat the respective surfaces, a support within thedrying chamber to position a mold section with each principal faceadjacent to one of said surfaces, conveying means to move said support 7her floor to define a slot along the side of the fer surfaces to theexit end of the drying chamber.

drying chamber, and a duct extending lengthwise along the drying chamberto convey away vapor evaporated from the mold section and escaping fromthe drying chamber through such slot beneath said apron.

11. In a mold drier, elements forming upper and lower heat transfersurfaces spaced apart to constitute a drying chamber, and each surfaceincluding an entrance section and an exit section, a support within thedrying chamber to'position a mold section with each principal faceadjacent to one of said surfaces, conveying means to move said supportlengthwise of the chamber continuously from the entrance end to the exitend thereof, heating means above the upper entrance section, and furtherheating means below the lower entrance sect-ion of said surfaces,adapted to heat such' sections for radiation of such heat into theentrance end of the drying chamber, and the exit sections of said upperand lower surfaces being remote from said heating means and of heatconducting material, operating to transfer heat out of the exit end-ofthe drying chamber where necessary, to

maintain a progressively decreasing temperature gradient over the exitsections of said heat trans- 12. The mold drying method which comprisessimultaneously exposing the parting surface and the back surface of agypsum base mold section for use as a casting matrix, eachto a proximatesource of direct radiant heat, the' temperature of such heat sources andthe time of mold section exposure thereto being suficient to dry fromthe mold section all chemically uncombined liquid and also to recalcine,at least partially, the gyp- K sum in the mold section, and thereaftergradually radiant heating surface in a close proximity thereto, movingthe mold in a.path parallel to such heating surfaces during suchexposure, and thereafter gradually cooling the mold by moving it betweenproximate heat conductive surfaces I sum in the mold section.

aeoacco of progressively lower temperature in the direction of moldmovement.

14. The mold drying methodwhich comprises exposing the parting surfaceand the back surface of a gypsum base mold section for use as a castingmatrix, each to a direct radiant heating surface at a temperature ofapproximately 1400 Fahrenheit and spaced from the respective moldsurfaces only a few inches, and thereafterexposing such surfaces of themold to heat conductive surfaces similarly spaced from the moldsurfaces, but at a temperature lower than 1400 Fahrenheit andsubstantially above room temperature, the combined exposure time beingof theorder of one and one half hours, thereby drying from the moldsection all chemically uncombined liquid and recalcining, at leastpartially, the gypsum in the mold.

15. The'mold drying method which comprises exposing the surface of amold composed of gypsum and asbestos, for use as a casting matrix, to aproximate source of direct radiant heat, the temperature of such heatsource and the time of mold exposure thereto being sufficient to dryfrom the mold all chemically uncombined liquid and also to recalcine, atleast partially, the gypsum in the mold.

16. The mold drying method which comprises exposing the parting surfaceand the back surface of a gypsum base mold section for use as a castingmatrix, formed of 100 parts, by weight,

of a mixture of asbestos pulp with calcined gypsum to approximately 160parts, byweight,

of water, each to aproximate source of direct sources and the time ofmold section exposure thereto being sufficient to dry from the moldsection all chemically uncombined water and also to 'recalcine, at leastpartially, the gypsum in the mold.

17. The mold drying method which comprises exposing the parting surfaceand the back surface of a mold section for use as a casting matrix,composed of gypsum base material combined with at least an equal weightof water, each to a direct radiant heating surface at a temperature ofapproximately 1400 Fahrenheit and equally spaced from the mold surfacesonly a few inches, thereby to preserve the mold section unwarped bysubstantially equal and concurrent evaporation of moisture from suchopposite surfaces, and thereafter exposing such surfaces of the mold toheat conductive surfaces also spaced from the mold surfaces only'a fewinches, but at progressively lower temperatures below 1400 Fahrenheitand substantially above room temperature, thereby minimizing the thermalshock to which the mold is subjected, the combined exposure time beingof theorder of one and one half hours, thereby drying from the moldsection all chemically uncombined liquid and also recalcining, at leastpartially, the gyp- HENRY F. HAGEMEYER;

